1. Field of the Invention
This invention relates to the field of support devices for animals, and in particular to mobile devices for injured or paraplegic animals such as dogs.
2. Description of the Prior Art
Suspensory apparatus for injured animals are known to the art of veterinary medicine. Dogs and other household animals are often hit by cars, and some breeds have developed a genetic predisposition to degeneration of intervertebral discs and spinal cord elements. Since the owners of injured animals are willing to go to great lengths to preserve the lives and happiness of their pets, a number of devices have been developed to allow animals to enjoy somewhat natural activities, notwithstanding severe injury or disease.
When a dog develops a debilitating rear limb disorder, or suffers spinal damage due to a traumatic encounter with an automobile, the art has not been entirely successful in providing a suitable orthosis to allow the animal to resume a natural life. A paraplegic animal is susceptible to secondary disorders and unless relatively natural motion can be provided, the animal will be further injured and debilitated due to inability to ambulate.
Applicant has formerly developed a mobile suspensory apparatus for supporting the rear quarters of injured animals. U.S. Pat. No. 3,406,661 discloses a cart having a vertical standard extending upwardly in a loop from an axle having two wheels. A length-adjustable yoke member is attached to the standard at or near the natural height of the animal's hips, and a hip support member comprising two attached horizontal loops, through which the animal's legs are inserted, is attached to the standard slightly above the yoke member.
A similar two-wheeled apparatus having side rods for connection to a harness is disclosed in U.S. Pat. No. 3,215,117-Short. The Short apparatus supports the animal's rear quarters at its abdomen, and the side rods position the wheels at a predetermined distance from the harness.
Alternate approaches are illustrated in U.S. Pat. Nos. 3,241,851-Dingbaum and 2,546,726-Creamer, Jr. These patents teach apparatus which employ the animal's body itself as a large part of the support structure. Both teach attachment of wheels to injured animals in a manner reminiscent of the attachment of training wheels to bicycles.
At the other extreme, U.S. Pat. No. 2,976,840-Hugus discloses a complete structure having four casters and associated structure supporting a sling which both encloses and supports the animal. The animal's rear legs are allowed to hang through holes in the sling.
All of the foregoing patents are intended to allow the animal to pull itself along by its front legs while its rear quarters are supported in a wheeled apparatus. Each design, however, has certain attributes which detract from the animal's ability to move in a natural way. In the devices which may be characterized as attaching wheels to the animal's rear quarters, there is little to maintain the wheels in the proper position for supporting the animal while walking. If the animal is severely crippled or paraplegic, the rear quarters would presumably be completely limp, and the wheels would tend to roll forward or backward with respect to the animal and the point of attachment to the animal. Accordingly, such devices are primarily useful for dogs which are only partially crippled. Another attribute of these designs which leads to the same conclusion is the fact that the animal's rear legs are positioned on the ground, and if completely limp would tend to drag or to interfere with the wheels, particularly if the animal backs up.
While moving naturally, the hips of an uninjured animal will trace generally sinusoidal paths in both vertical and horizontal planes. Since wheeled suspensory apparatus for supporting the animal's rear quarters will maintain the rear quarters along a line parallel to the ground, at best the animal will, of necessity, move in a slightly unnatural way. Moreover, in order to avoid dragging the feet of animals supported in such wheeled apparatus, it has been formerly necessary to position the member supporting the rear quarters to a level high enough to hold the rear feet off the ground and possibly clear of the wheels. The references cited hereinabove each depict the animal's rear feet at or very near the ground. The one exception is Hugus, which shows the animal's rear legs hanging above their natural position, the legs being shown somewhat retracted. Of course a paraplegic animal is unable to retract its legs. In addition, in the situation where an animal retains some residual control of its rear quarters, the animal will instinctively attempt to use its legs in walking, whether suspended or not. Such movement further interferes with the wheels and axle, and with natural movement. Where an animal is completely limp, prior art devices have either held the rear quarters unnaturally high, or have allowed the feet to drag and/or interfere with the axle and wheels of the device.
U.S. Pat. Nos. 3,406,661-Parkes and 3,215,117-Short teach two-wheeled carts having a vertical standard upon which a yoke or harness is attached. The rear quarters are supported in each device by members interfacing with the animal's rear parts. Inasmuch as the weight of the rear quarters is supported forward of the vertical plane including the axle, a downward pressure is exerted on the yoke or harness. In addition, due to such positioning, the apparatus each have a tendency to rotate forward about the axle. Any downward force at the shoulders further detracts from the animal's ability to move around freely and naturally.
The foregoing tendency would be reversed if the animal backed up, or if the apparatus was adjusted such that the rear quarters were supported somewhere to the rear of a vertical plane including the axle. In this event, the apparatus could be expected to exert a force upward on the yoke, and to tend to rotate the apparatus rearward about the axle, raising the shoulders. If severely misadjusted or if the animal should hit an obstacle, the apparatus could be overbalanced and could fall over backwards. In any event, the force would detract from natural movement. Presumably, either apparatus could be adjusted to position the hips over the axle, but the hip position and the nature of the disclosed structures make the balance precarious and adjustment inconvenient and ineffective.
In light of the foregoing, it is apparent that there is a need to adapt mobile suspensory apparatus to the dynamics of the animal. The apparatus should be effective to support the rear quarters of the animal in as near a natural position as possible, yet should be convenient to adjust and insensitive to errors in adjustment. This requires that the device be balanced to achieve a minimum force either upwards or downwards at the yoke. There has also been a need to adapt such suspensory apparatus to the alternative situations in which (1) the animal's rear quarters are completely limp and (2) the animal's rear quarters retain some residual movement.
The present invention accomplishes these goals by an apparatus which allows the rear quarters of the animal to be positioned at a natural level vertically with respect to the thorax of the animal, yet prevents the feet from dragging or interfering with the wheels. An embodiment is adapted to the situation in which residual movement is retained, and a second embodiment directed to completely limp rear quarters. The apparatus includes a convenient means for selectively positioning the axle at a range of positions, to balance the apparatus for a minimum of force on the yoke and to reduce the tendency to become misadjusted or overbalanced in use.